Cable operators have widely deployed high-speed data services on cable television systems. These data services allow subscriber-side devices, such as personal computers, to communicate over an ordinary cable TV network Hybrid Fiber Coax (HFC) cable. A Cable Modem Termination System (CMTS) connects the cable TV network to a data network, such as the Internet. The Data Over Cable Service Interface Specification (DOCSIS) is one of the cable modem standards used for transferring data over the cable TV network.
To ensure reachability between the CMTS and its cable modems, ranging transactions are frequently performed. Ranging allows the cable modem to fine-tune its physical upstream transmission parameters to better adapt to gradual changes that could lead to channel impairment, and thus remain reachable by the CMTS. Successful ranging involves the CMTS sending a message to define a transmission window for the cable modem to send a ranging request, the cable modem sending the ranging request during the transmission window, and the CMTS responding back with a ranging response.
If the cable modem does not send the ranging request during the transmit window, the CMTS provides another transmit window. If this process repeats too many times (typically sixteen), the CMTS marks the cable modem offline and cleans up resources so that these resources can be available for other cable modems.
When a cable modem is operating in Multiple Transmit Channel (MTC) mode, the cable modem periodically ranges on more than one active upstream transmit channel. If these ranging transactions are performed as frequently on a per-channel basis as a cable modem operating in non-MTC mode, the CMTS can become over-utilized. The disclosure that follows solves this and other problems.